Respiratory System Overview

Respiratory System Learning Outcomes

• Students will understand the anatomy of the respiratory system.
• Students will understand the function of the respiratory system.
• Students will understand the process of gas exchange and gas transport.
• Students will understand the regulation of respiration.

Respiratory System Divisions

• The respiratory system is divided into the upper and lower respiratory tract.
• The upper respiratory tract includes the nose, pharynx, nasal cavity, and paranasal sinuses.
• The lower respiratory tract includes the larynx, trachea, bronchi, bronchioles, and alveoli.

Conducting Zone

• The conducting zone consists of structures that transport air.
• These structures do not participate in gas exchange.
• These structures include the nasal cavity, nasopharynx, oropharynx, laryngopharynx, larynx, trachea, bronchi, and all bronchioles except for respiratory bronchioles.
• They are responsible for transporting, filtering, humidifying, and warming air.

Respiratory Zone

• The respiratory zone includes structures where gas exchange occurs.
• The sites of gas exchange are called alveoli (singular: alveolus).
• All respiratory zone structures contain alveoli, including respiratory bronchioles, alveolar ducts, and alveolar sacs.

Nasal Cavity

• The nasal septum divides the nasal cavity.
• The hard palate forms the floor of the nasal cavity and separates it from the oral cavity.
• Bony ridges called conchae increase the surface area of the nasal cavity, causing air to churn.

Paranasal Sinuses

• Paranasal sinuses open into the nasal cavity and are lined with mucous membranes.
• Nasolacrimal ducts connect the eyes to the nasal cavity.
• Olfactory receptors are located in the superior part of the nasal cavity.
• Lining of the cavity is with stratified squamous epithelium and coarse hair to trap dust or large particles.
• Near the pharynx, the cavity is lined by pseudostratified columnar cells associated with goblet cells for a sneeze reflex.

The Pharynx

• The pharynx is shared by the digestive and respiratory systems.
• It is divided into three sections:
• Nasopharynx (pseudostratified columnar – superior portion ; enclosed by uvulva during swallowing)
• Oropharynx (Stratified squamous) – continuous with the oral cavity
• Laryngopharynx – from tip of epiglottis until esophagus

Trachea

• The trachea extends from the larynx to the mediastinum, dividing into left and right primary bronchi at the 5th thoracic vertebra.
• The trachea is lined by pseudostratified epithelium associated with goblet cells to secrete mucus due to abundant seromucous glands.
• It is supported by 16-20 C-shaped hyaline cartilage rings.
• The posterior wall of the trachea has no cartilage, is of connective tissue and smooth muscle, enabling it to contract during coughing.
• The trachea provides the esophagus with space to expand when large food boluses are swallowed.
• The last tracheal cartilage is expanded and contains a sensitive projection known as the carina.
• The mucous membrane in the carina is the most sensitive area of the larynx and trachea, triggering the cough reflex.
• The right primary bronchus is more vertical, shorter, and broader than the left.

Bronchi

• The trachea divides into two main bronchi, right and left.
• The right bronchus is wider, shorter, and more vertical than the left, making it more prone to foreign object obstruction.
• The bronchi are lined by pseudostratified columnar epithelium and supported by C-shaped cartilage.
• Air reaching the bronchi is filtered, warmed, and humidified.

Bronchial Tree

• The main bronchi divide into lobar (secondary) bronchi.
• The right lung has three lobar bronchi, one for each lobe.
• The left lung has two lobar bronchi.
• Lobar bronchi divide further into segmental (tertiary) bronchi, creating smaller and smaller bronchi (approximately 23 branchings).
• Tertiary bronchi supply air to a single bronchopulmonary segment.
• Passageways with a diameter less than 1 mm are called bronchioles.

Bronchioles

• Terminal bronchioles are the last bronchioles without alveoli.
• Bronchioles with alveoli are called respiratory bronchioles and lead into alveolar ducts.
• Cartilage is absent in the walls, and smooth muscle increases with branching, allowing for relaxation and contraction to control air passageway diameters.

Lungs

• Lungs consist of lobes separated by fissures. The right lung has three lobes, the left lung has two.
• The left lung has a concave medial surface with a cardiac notch.

Alveolar Ducts and Alveoli

• Respiratory bronchioles terminate in alveolar ducts and sacs (respiratory membrane), each with many openings into alveoli, small air sacs.
• The respiratory membrane consists of a thin layer of fluid, alveolar epithelium (squamous epithelium), basement membrane, interstitial space, basement membrane of capillary endothelium, and capillary endothelium (squamous epithelium). Six layers total.

Alveolar Cells

• Alveolar cells (Type I pneumocytes) line the alveolar surface.
• Septal cells (Type II pneumocytes) secrete surfactant to reduce surface tension.
• Alveolar macrophages (dust cells) engulf foreign particles.

Pleural Cavities and Membranes

• Each lung is enclosed by a pleura, which is a serous membrane.
• The pleura consists of two layers:
• Parietal pleura: lines the walls of the pleural cavity.
• Visceral pleura: adheres to the surface of the lungs.
• Pleural fluid fills the space between the pleura, lubricating them for movement with little friction.

Pressure Changes During Inhalation and Exhalation

• Intrapulmonary pressure, the pressure inside the lungs, and atmospheric pressure together determine airflow direction.
• Intrapleural pressure, the pressure within the space between the parietal and visceral pleura always needs to remain lower than alveolar pressure to prevent collapse of the alveoli.

Pulmonary Ventilation

• This is the process of moving air into and out of the lungs.
• It relies on Boyle's Law: pressure and volume are inversely related.
• Changes in the diaphragm and rib cage volume alter pressure, causing air to flow into or out of the lungs during inspiration and expiration.

Respiration

• There are 4 processes involved in respiration:
• Pulmonary ventilation (moving air into and out of the lungs).
• External respiration (movement of O2 from lungs to blood, CO2 from blood to lungs).
• Gas transport (Mechanism of moving O2 and CO2 through blood).
• Internal respiration (movement of O2 from the blood to the cell interior, CO2 from cell interior to the blood).

Gas Laws in Respiration

• Dalton's law describes how individual gases exert pressure in a mixture, proportional to their abundance.
• Henry's law explains that the amount of gas dissolved in a liquid is directly proportionate to its partial pressure.

Gas Exchange

• Differences in partial pressure drive gas exchange across the respiratory membrane.
• Small diffusion distance, soluble gases, large surface area and coordination of blood flow and airflow make gas exchange efficient across the respiratory membranes.

Oxygen Transport

• Oxygen is primarily transported bound to hemoglobin in red blood cells (RBCs).
• P02, pH, temperature and fetal hemoglobin are factors that affect how much oxygen is carried in hemoglobin.

Carbon Dioxide Transport

• Carbon dioxide transport involves plasma dissolution, carbonic acid formation, and binding to hemoglobin to form carbaminohemoglobin.

Respiratory Centers of the Brain

• Medullary centers (DRG and VRG) set the pace of respiration rhythmically.
• Pons regulate respiratory centers with apneustic and pneumotaxic centers.

Respiratory Reflexes

• Chemoreceptors reflex adjust respiration rates based on levels of carbon dioxide, oxygen, and pH.
• Baroreceptors reflexes adjust respiratory rates based on blood pressure
• Protective reflexes such as cough and sneeze reflexes.
• Higher brain centers such as cerebral cortex and limbic system can influence the rate and rhythm.

Voluntary Control of Respiration

• Conscious thought can affect the respiratory rate.
• Emotional states, through signals from the limbic system, can affect respiration by influencing either sympathetic or parasympathetic nervous system.

Aging and the Respiratory System

• The efficiency of the respiratory system decreases with age.
• Elastic tissue in lungs deteriorates, reducing lung compliance and vital capacity.
• Chest movements, sometimes restricted by arthritic changes, impact respiratory function.
• Some degree of emphysema commonly happens.

Respiratory Diseases

• Smoking is a major cause of diseases affecting lung function.
• Chronic bronchitis, characterized by bronchial edema, chronic, productive cough, and bronchospasm.
• Emphysema involves destruction of alveolar walls, lung fibrosis, and air trapping.